1. Field of the Invention
The present invention relates to a fuel cutoff valve for mounting onto the upper wall of a fuel tank to open and close a fuel conduit that connects the fuel tank to the outside to facilitate removal of fuel vapors from the fuel tank.
2. Description of Related Art
Fuel cutoff valves of this kind are known in the art, being described in JPA 11-315765, which has the structure depicted in FIG. 11. As will be apparent from the sectional view in FIG. 11, the fuel cutoff valve 100 is mounted on the upper tank wall FTa of a fuel tank FT, and comprises a casing 102, a cover 110, a float 120, and a spring 130. The casing 102 comprises a top wall 103, a side wall 104 integrally formed with outside edge of top wall 103, and a base plate 105 attached to the bottom end of side wall 104 so as to define an internal space constituting a valve chest 102S. Within valve chest 102S is housed a float 120 having a valve portion 120a in its upper portion. This valve portion 120a opens and closes a fuel conduit 103d connected to the outside of fuel tank FT. The float 120 is supported by a spring 130 arranged on the base plate 105.
The cover 110 comprises a cover main body 112 for attachment to the casing 102, a cover passage forming portion 114, and a flange 115, these elements being of unitary construction. The cover 110 is a separate element from the casing 102 and is assembled with the casing by fitting the two together. A leak-prevention rib 122 is interposed between casing 102 and cover 110 to create a labyrinth structure providing increased mating surface area for sealing.
When the fuel tank FT is being filled, fuel vapor present within fuel tank FT flows to the outside (canister) via a through-hole 105a formed in the base plate 105 of casing 102, a through-hole (not shown) in side wall 104, the valve chest 102S, the fuel conduit 130d, and the passage 114a in cover 110. When the fuel entering fuel tank FT reaches a predetermined level FL1, fuel flows into valve chest 102S via through-hole 105a, providing a buoyant force that causes the float 120 to rise. The rise of float 120 causes the valve portion 120a formed in the top portion of float 120 to block fuel conduit 103d, preventing fuel from flowing out from the fuel tank FT.
With the fuel cutoff valve 100 described above, however, the cover 110 and casing 102 are assembled together via a leak-prevention rib 122. Accordingly, if the gap therebetween is small, the cover 110 and casing 102 will be difficult to assemble. Conversely, if the gap is made larger in order to facilitate assembly, a poor seal will result. The conventional fuel cutoff valve 100 thus has the drawback that it is difficult to simultaneously provide a better seal while attempting to improve the ease of assembly.
An aspect of this invention is to provide a fuel cutoff valve featuring a simplified assembly operation as well as an excellent seal.
Specifically, the first embodiment of the present invention provides for a fuel cutoff valve for mounting on the upper tank wall of a fuel tank having a cover, casing and valve body. The upper portion of the casing constitutes an insert member having a plurality of sealing ribs projecting substantially vertically towards the cover, and a stopper formation extending at substantially right angles to the sealing ribs. The cover is unified with the upper portion of the casing by means of overmolding such that said sealing ribs and stopper formation are embedded in the cover. The cover is fabricated of a first resin material that is thermally weldable to the upper tank wall. The cover has an annular welding end for thermal welding onto the upper tank wall and a passageway for removing fuel vapor from the fuel tank. The casing is made of a second resin material different from the first resin material. The casing is further provided with a valve chest that connects the fuel tank interior to a fuel conduit connecting the fuel tank interior to the outside to facilitate fuel vapor removal. The valve body is housed within the valve chest and opens or closes off the fuel conduit depending on the fuel level in said fuel tank.
The valve body housed within this valve chest rises and falls with changes in buoyant force produced by changes in fuel level within the fuel tank. When the valve body rises due to buoyant force, it closes off the fuel conduit, preventing outflow of fuel from the tank. The cover is made of a resin material that is thermally weldable to the top of the tank, and is mounted onto the tank by means of thermal welding to the upper tank wall. In this way, the need for a fastening member on the top of the fuel tank is obviated, allowing for easy mounting of the fuel cutoff valve.
The casing is made of a different resin material than the cover, which is specifically a resin having better resistance to fuel swelling than the cover, to improve sealing in the seat portion, etc. The casing consists of a resin material that is not welded to the cover, but is unified with the cover by means of overmolding. Specifically, the casing constitutes an insert member having a plurality of sealing ribs projecting substantially vertically or upward towards the cover, and a stopper formation extending at substantially right angles to the sealing ribs, the cover being unified with the upper portion of the casing by overmolding such that the sealing ribs and stopper formation are embedded in the cover. As used herein, overmolding refers to a process wherein, after initially molding the cover or casing, the companion part is formed by injection molding in such a way as to partially enclose the first part; it includes various processes such as insert molding and two-color molding. Since the casing is used as an insert member and is integrally formed with the cover, the two resin materials, while not being welded together, fit together tightly so that fuel cannot leak out between them. The labyrinth structure created by the plurality of sealing ribs provides an extended passage for fuel vapors, affording reduced passage of fuel.
The cover experiences greater swelling by fuel in the fuel tank than does the casing, which has the effect of reducing the gaps at the locations of the sealing ribs and thereby increasing the connecting force thereof to the casing, affording even greater reductions in passage of fuel.
The stopper formation is at least one substantially horizontal step that extends at substantially a right angle to the sealing ribs and provides secure attachment between the cover and the casing in effect locking these elements together. The horizontal step includes but is not limited to a protruding member, a stopper hole that includes a recess or through-hole subsequently filled by overmolding, or a combination thereof. This obviates the need for structures that include engagement tabs or the like for attaching the cover and the casing together, so as to provide a simpler structure. Therefore the casing does not give rise to problems associated with chatter against the cover, namely, reduced mechanical strength to resist impact and change in the liquid level at which the fuel cutoff valve opens and closes, thereby providing stable opening and closing characteristics.
The sealing ribs are composed of a plurality of divided arcuate projecting portions in an annular configuration. These arcuate projecting portions are arranged such that the gaps separating them from their neighbors do not lie on straight lines passing through the centers of concentric circles. By means of this structure, resin flowing into the sealing ribs and stopper formation may proceed smoothly during overmolding of the cover onto the upper portion of the casing, thereby avoiding filling defects.
In another embodiment, the upper portion of the casing is further provided with an outer rib situated to the outside of the sealing ribs across a predetermined gap. The outer rib projects out such that it is integrally linked in an annular configuration. Since the outer rib is integrally linked in an annular configuration, mechanical strength to resist injection pressure during the overmolding process is high, and the casing and cover may be securely attached without falling over. Also, this annular configuration of the outer rib provides an improved gas-tightness relative to the sealing ribs, which are arcuate projecting portions.
The outer rib can be provided with a recess, a through-hole or a projection extending from the center of the casing to its outside wall. Since the recess, a through-hole or a projection in the outer rib becomes filled with the resin of the cover during fabrication of the cover by overmolding, the cover may be attached more securely to the upper portion of the casing through the use of such stopper formations.
A flash eliminating rib can also be provided along the circumference of the outside wall of the casing, at joining locations with the cover. The flash eliminating rib has the effect of blocking the flow of molten resin along the outside wall of the casing during fabrication of the cover by overmolding thereby reducing the amount of flash which forms.
Where the upper tank wall is polyethylene, the first resin may consist of the same polyethylene as the upper tank wall and the second resin material may consist of a polyacetal or polyamide having excellent resistance to fuel swelling.
The invention also encompasses a fuel cutoff valve for mounting on the upper tank wall of a fuel tank having a cover, a casing, and a valve body. The cover, rather than the casing, constitutes an insert member having a plurality of sealing ribs projecting substantially vertically towards the casing and a stopper formation extending at substantially right angles to the sealing ribs. The casing is unified with said cover by means of overmolding such that said sealing ribs and stopper formation are embedded in the casing. The cover is fabricated of a first resin material that is thermally weldable to the upper tank wall. The cover has an annular welding end for thermal welding onto the upper tank wall and a fuel conduit. The casing is made of a second resin material different from the first resin material. It is provided with a valve chest, which connects the fuel tank interior with the fuel conduit. The fuel conduit connects the fuel tank to the outside. In this variation of the invention, the fuel conduit at least in part has a connecting passage located in the casing that connects the fuel tan to an area outside of the fuel cutoff valve thereby effectuating vapor removal from the fuel tank. The valve body is housed within the valve chest and opens or closes off the fuel conduit depending on the fuel level in said fuel tank.
The fuel cutoff valve pertaining to this modification of the invention has sealing ribs and a stopper formation formed on the cover, the sealing ribs and stopper formation being overmolded to form the casing. Like the previously described embodiments, this modification affords secure attachment of the cover and casing.
Additionally, the present invention provides for the combination of a fuel tank comprising a resin upper tank wall having a fixation hole and a fuel cutoff valve mounted on the upper tank wall by insertion thereof partway into the fixation hole. The fuel cutoff valve has a cover, a casing and a valve body such that the upper portion of the casing constitutes an insert member having a plurality of sealing ribs projecting substantially vertically towards the cover and a stopper formation extending at substantially right angles to the sealing ribs. The cover is unified with the upper portion of the casing by means of overmolding such that the sealing ribs and stopper formation are embedded in the cover. The cover is fabricated of a first resin material that is thermally weldable to the upper tank wall and has a welding end for thermal welding onto the upper tank wall. As with all embodiments and modifications of the present invention, the cover may have a passageway that connects to or may be part of the fuel conduit connecting the interior of the fuel tank to the outside, thus facilitating fuel vapor removal. The casing is made of a second resin material different from the first resin material, and is provided with a valve chest connecting the fuel tank interior with the fuel conduit including a connecting passage of the casing which then connects to a tubular member or other passageway in the cover. The valve body is housed within the valve chest and opens or closes off the fuel conduit depending on the fuel level in said fuel tank.
The present invention also provides a process for manufacturing a fuel cutoff valve. A cover is fabricated from a first resin material that is thermally weldable to the upper tank wall, and has welding end for thermal welding onto the upper tank wall. The casing is formed from a second resin material different from the first resin material and has a fuel conduit. The casing has a plurality of sealing ribs projecting substantially vertically towards the cover and a stopper formation extending at substantially right angles to the sealing ribs are formed in the upper portion of the casing. The portion of the casing having the sealing ribs and stopper formation is set in the cavity of a mold. Then the cover is integrally molded with the upper portion of the casing by means of overmolding through injection of the first resin material into the cavity. This process for manufacturing the fuel cutoff valve may be used to form the embodiments of the present invention.